Operation of Continuous Miners (CM) is one of the most dangerous jobs in the coal mining industry. Fatalities and injuries to mining personnel working in the vicinity of CMs are a major concern to both the industry and to the government health and safety organizations, Mine Safety and Health Administration (MSHA), and the National Institute of Safety and Health (NIOSH). MSHA and NIOSH have initiatives and programs under way to try to improve the health and safety of personnel working around CMs. Further improvements are not likely to be made by better procedures and controls alone, better technical tools being needed. The operational conditions for CMs are especially complex and challenging and produce unique hazardous conditions. Some technical solutions to these difficult safety and health hazards around CMs are applicable to other work environments involving mobile equipment.
The hazards and health concerns for CM operators and other workers are many and need to be explained in order to understand the associated problems and solutions. They can be generally divided into three categories. One category are the health and safety concerns associated with the cutting process. Another category is associated with moving the CM from one position to another, called tramming, which is necessary and frequent, and movements of the cutter boom and loading boom. The third category is performing maintenance or other operations on the CM. For purposes of this specification, the third category can be grouped with the hazards associated with category two. One factor in common with all these hazards is the proximity of personnel to the CM and/or to the geologic formation in which the CM is operating.
During cutting, operators typically position themselves as far forward toward the mineral face as safety rules will allow so that they can better see, hear, and feel the vibrations from the cutting process. The most challenging phase of their cutting control task is when the cutter drum is shearing down toward the floor because the view of the front area of the miner is obstructed by the miner itself and by dust and water sprays. When cutting around a corner during a crosscut, the view is further obstructed by a pillar. After frequently being in a forward position, at the side of the CM, it becomes a comfort zone and the operator develops a habit of remaining in that position, even when tramming.
In recent times fatalities and serious injuries have resulted from metallic objects being thrown from the cutter, hitting personnel. Rocks or coal sometimes fall from a freshly cut wall or roof, seriously injuring or resulting in fatalities, even when the operators are behind two roof bolts, which is required by safety rules. Positions further from the coal face are less hazardous. The NIOSH, a division of the Center for Disease Control, studies and reports on the serious health hazards from CM produced dust and noise. It is rather obvious that the safety and health of the operators would be improved if they were positioned further from the CM and the coal face being cut. Not only is there a need for a method of keeping personnel further away from the hazards, there is also a need to help the operator to develop safer habits.
It has already been made possible to re-position the operator further from the CM and the mineral face, during cutting, through the use of Armored Rock Detectors and Geosteering techniques as described in U.S. Pat. Nos. 6,781,130 and 6,435,619, which are incorporated herein in their entireties. However, even if this capability, now available to the industry, were being widely used, experience has shown that operators may continue to move unnecessarily close to the CM and to the mineral face. A proximity system is needed for use in conjunction with Geosteering to provide protection to miners during all CM activities.
Because of the significant number of fatalities resulting from crushing by CMs, the MSHA has made the development of an effective proximity system their highest priority safety initiative. Historically, the greatest concern has been for the CM operator since he is constrained to be in the vicinity of the CM at all times. However, personnel other than the operator are sometimes crushed by the CM, and their safety should be protected equally well. A major reason for other personnel being dangerously close to the CM is in order to help move the power cable trailing behind the CMs through which they obtain their electrical power. The CM is used to drag the heavy cables as it is moved from one cut to another, which is typically required many times during a work shift. As workers attach cable straps to the CM, they must essentially touch the CM. Although the CM should be stopped until after the worker has completed his task, mistakes are made. Whether due to operator error or equipment failure or a combination of these factors, these workers are sometimes crushed before they leave the hazardous area. Since the length of CM crawler tracks are short relative to the length of the overall CM, each end of the CM can move quickly, giving little time for a worker to move away. Also, personnel may approach the CM in order to make an adjustment or for maintenance purposes. The two booms of the CM may be moved or be articulated such that a worker is crushed against the wall or roof. Incidents like these, and others, could not occur if CM movements were stopped when the CM is dangerously close to any worker. Therefore, there needs to be an automatic method of stopping the CM movements if the CM is too close to a worker. A worker should be able to make a Panic Call to stop the CM if a hazardous condition is being created for himself or others.
Though the safety challenges for the CM are generally more operationally complex than for mobile machines used in most other industries, overcoming these challenges has produced technology that can improve the safety of other mobile equipment, including trucks, tractors, fork lifts, rollers, etc. Even within the underground mining operations, there is a need for an effective proximity system for use on shuttle cars, pinning machines, rides, and other moving equipment. There is also a need for an effective method of preventing personnel from entering un-supported roof areas, conveyors, and such which can benefit from this same technology.
It should be pointed out that many types of proximity devices and systems have been used through the years. None are very effective for underground mining applications and have been only moderately successful in some other industries. In many cases, these devices and systems have been passive types that have not included an active element worn by the person being protected. Nuisance alarms are a common problem which reduces the effectiveness of some systems.
Important progress was made with the proximity concepts offered by the Schiffbauer U.S. Pat. Nos. 5,939,986 and 6,810,353, which are incorporated herein in their entireties. However, there are significant deficiencies in these concepts. Important issues and technical problems must be resolved before they can be made effective for underground mining applications. Novel solutions are required. For example, in order to provide a magnetic marker field around all or most all of a CM, multiple generators are required. According to the '986 patent, multiple loop antennas may be driven with a single alternating current source. Not addressed are requirements for positioning, orienting, and phasing of the loops to produce fields that are complimentary and not mutually destructive. Loops are difficult to protect in the harsh environment on a CM. They must be placed in a plane that is generally parallel to the outer surface of the CM to avoid damage. If oriented perpendicular to the CM, they will soon be ripped off. Any item attached to the outer surface of a CM must be specially designed and protected. Most locations on a CM are such that a loop in any orientation will require carefully designed protection. Structural elements used to protect the loops alter the shape of the fields, though not as much for low frequencies as for higher frequencies. The fields produced by adjacent loops will vary according to the separation of the loops and the distance from the loops. Taking all these variables in combination, one can readily conclude that the use of multiple loops to produce a single, uniform marker field is not easy to accomplish. Adjustment of fields generated by loops can be difficult and time consuming, at best. An earlier approach was to use a single loop around the entire CM body. Protection of such a loop is difficult to achieve and once installed such a loop reduces access to CM equipment. Providing sufficient driving power, combined with the difficulty in tuning the coil to resonance, creates a very challenging situation. Another general concern with loops that are to be close to the coal face, carrying large circulating currents and resonance-produced voltages is that they are being used in an atmosphere that may, from time to time, be explosive. It is desirable for such devices to be contained within explosion proof (X/P) housings. Placing such loops inside an X/P housing is not feasible due to size and other factors.
In the Schiffbauer '353 patent mention is made of the possible use of a ferrite as the inductor for producing the magnetic marker field, rather than a loop, though no details are supplied. Practical and crucial considerations of how to design the ferrite “antennas” so that they can be effectively protected, properly positioned, properly oriented, and how to control the phasing of multiple ferrite “antennas” are not addressed. As explained above, the profile of the “antennas” must be made as low as possible while, at the same time, providing shielding from the mining materials and the walls. They must be properly spaced so that they must be made capable of withstanding the environment at the installed location. Also, if separate signals are provided for each ferrite, as implied by the '353 patent, there will be a phasing problem. Since all of the set of “antennas” must operate within a relatively small bandpass produced by the required resonant circuits, some of the units are likely to be operating at frequencies that are nearly the same. The beat frequencies in the magnetic field will produce fluctuations in the field strength readings by the alarm devices carried by the workers, which is the basis for determining when a worker is within a hazardous zone. One could attempt to provide a minimum separation between the frequencies of all marker field generator units. But, there are obvious practical problems with providing sufficient frequency separation between units, particularly when there is a limited bandwidth. A method of avoiding beat frequencies in the marker field is needed.
In the Schiffbauer '353 patent, a device, called a “receiver” was described that had ferrites wound with copper coils that were used to sense a marker field, circuits to measure its strength, circuits to make a decision if the “receiver” was in a Warning Zone or in a Stop Zone. It also contemplated the need to send warning or stop decisions to the mobile equipment to be acted upon. But, there are important problems to be solved before this concept can become a practical system for use on a continuous miner. For example, critical timing problems posed by simultaneously operated multiple “receivers” must be solved to prevent the signals from the “receivers” from interfering with each other when they transmit data or commands to the CM. After more study into the safety problem being solved, it is apparent that additional capability is needed. For example, the worker needs to be able to give commands to the CM to identify the operator in charge, to reset the system after the CM has been stopped by the system, and other commands, all without having to enter the warning or stop zone around the CM in order to reach the controls on the CM. There is a need to provide an identification (I.D.) for each “receiver” and to record data for each “receiver” in range. The worker needs to be given a sense of urgency by his alarm if a CM is approaching. The operator needs to know if there is a miner in range who has a low battery voltage in his personal alarm, and each such safety event should be recorded. The strength of the marker field being measured by the “receiver” needs to be transmitted to the CM for recording for use in investigations of incidents. Most, if not all of these needs have to be met in satisfactory manner so that the total system is user friendly and effective.
There is also a need for an integrated system concept not addressed by the prior art, and a need for other capabilities not considered. Many operational rules and procedures have been employed to improve miner safety. Countless safety features have been designed into modern mining equipment. However, even with these many innovations, communications between mining machines and between personnel moving from place to place in the mine continue to have serious shortcomings. An example is when the operation of one CM should result in constraining the operation of another. This can exist whenever two CMs are operating within the same mining unit, sometimes referred to as a super unit. Ventilation requirements often specify that two CMs in the same unit not be cutting coal simultaneously. Verbal coordination is not sufficiently dependable and currently available techniques for interlocking the CMs are complex, costly, and troublesome. A better system is needed.
Much progress has been made by the American mining industry in eliminating underground explosions and fires and other disastrous situations, but they sometimes occur. Frequently, immediately after such events, location of the workers is very difficult and sometimes impossible because the workers move around as they work, and their equipment is moving as well. Even though numerous communication devices have been employed, using many different technologies and approaches, communications problems remain. In particular, there is a need to provide better reporting of the location of personnel within the mine and to do so in a way that is transparent to the worker so as to not impact his activities or to be distracting. Finally, it is desirable that all safety improvements be implemented in such a way that reduces stress on the worker.
Finally, one of the reasons that some potentially useful communication devices are not employed is due to the difficulty of keeping the devices properly positioned in the mine and of keeping them operational under such difficult circumstances. In some locations, power is not available so that portable generators having an internal battery supply are needed. Also, proliferation of safety and communications devices can cause confusion and complexity which detracts somewhat from safety. These safety innovations need to be combined in a more effective manner than has not been achieved in the past.